Hi John,
I would doubt that the query is sufficient for this. AFAIK, you would at least need to exclude all value entries of the type "revaluation" for the quantities, becauso there you also have Item Ledger Entry Quantity filled in. Also, the report 5899 seems to do some not-so easy to understand things with calculating the remaining quantity at date, and adding up the proportional amount with respect to the valued quantity. But I think this calculation also has a bug, as I write here: community.dynamics.com/.../106259.aspx
If it turns out that you can simply add up all value entries of the item regardless of application, then your way would be a possible and fast solution. But this can also be achieved in NAV at (almost) the same speed, you only need to ignore the selection process that is implemented in R 5899 / T32. I would not suggest to do this, I don't know enough about it. But I will read the whitepaper on costing for NAV 2013, maybe there is a clue for this implementation.
with best regards
Jens